When it was mentioned to Ibn Shihab (al-Zuhri) that fasting on Saturday had been prohibited, he would say: This is a Himsi tradition.
Sunan Abi Dawud Book 14, Hadith 111
← Previous Hadith That the Prophet (ﷺ) entered upon her on Friday while she was fasting. He asked: Did you fast yesterday ? She said: No. He again asked: Do you intend to fast tomorrow ? She said: No. He said: So break your fast.

Sunan Abi Dawud Book 14, Hadith 110 Next Hadith → I always concealed it, but I found that it became known widely, that is, the tradition on Ibn Busr about fasting on Saturday.

Abu Dawud said: Malik said: This is a false (tradition).

Sunan Abi Dawud Book 14, Hadith 112